1. Field of the Invention
The present invention relates to a position detecting device of a linear motor, which enables the linear motor to carry out position detection and position control alone without a linear scale provided in parallel arrangement for controlling the linear motor, by utilizing the magnet arrangement constituting the linear motor itself as the linear scale for positioning.
2. Description of the Related Art
The linear motor according to the prior art either utilizes a separately provided linear scale arranged in parallel with the linear motor, or comprises a stator constituting the linear motor having two kinds of magnets with different surface magnetism arranged alternately and at uniform intervals along a linear moving direction, and a coil disposed movably in the linear direction while maintaining a uniform distance from the surface of the magnets constituting the stator, wherein the induced voltage occurring between the magnet and coil is detected, and thereby, the position of a moving member with respect to the stator is detected by computing the displacement of induced voltage (refer for example to Japanese Patent No. 3396216 (patent document 1) and Japanese Patent Application Laid-Open Publication No. 2002-281783 (patent document 2).
According to the prior art where a linear motor and a linear scale are used together, it was necessary to provide a mounting means for precisely positioning the linear scale to the linear motor, and to provide a means to block water and dust from entering. Moreover, the assembling of the above means had to be performed with high accuracy, which required high costs even equivalent to the cost for building the linear motor itself.
According to patent document 1 which incorporates the function of a linear scale into the linear motor, the magnets arranged at uniform intervals and constituting the stator are used as a scale, so that if the magnets or the intervals contained errors, such errors were transferred completely as scale errors and deteriorated the scale accuracy.
In practice, it is impossible to form magnets without size errors or to arrange the magnets at uniform intervals without error. So the magnet arrangement inevitably contained some error, limiting the accuracy of the scale.